1. Field of the Invention
The invention relates to a pigment dispersion composition capable of being utilized in imaging materials such as color filters and color proofs, and photocurable materials such as ink and paint; a photocurable composition appropriate for forming a color filter for a liquid crystal display and a solid-state image sensing device; a color filter using the photocurable composition; and a method of production thereof.
2. Description of the Related Art
In recent years, applications of color filters in liquid crystal displays (LCDs), have expanded beyond monitors to include televisions and the like. Accordingly, high specification color properties with respect to chromaticity and contrast have been desired. Similarly, high quality color properties such as reductions in color irregularities and improvements in color separation have been demanded for applications of image sensors (solid-state image sensing devices).
In relation to the above, there has arisen a demand that pigment be dispersed in a minuter state (favorable dispersibility) and that pigment be retained in a stable dispersion state (favorable dispersion stability). If dispersibility is insufficient, fringes (notches in an edge portion) and surface irregularities are caused in a formed colored resist film, and problems occur, such as a decrease in chromaticity and dimensional accuracy of a color filter to be produced, and a remarkable decrease in contrast. If dispersion stability is insufficient, the following problems in particular are easily caused during the production processes of a color filter: uniformity of film thickness is decreased in a process of applying a colored photocurable composition; photosensitivity is decreased in a process of exposing; and alkali solubility is decreased in a process of developing. In addition, when dispersion stability of a pigment is poor, the components of a colored photocurable composition cohere and increase the viscosity thereof over time and significantly decrease pot life, which is problematic.
In order to address such problems, a pigment dispersant comprising a polymer combined with an organic pigment has been proposed (refer to Japanese Patent Application Laid-Open (JP-A) No. 4-139262). The use of a copolymer containing acid groups such as carboxylic acid and a radical of sulfonic acid or the like, and a polymer containing maleimide substituted with a phenolic acid group has also been proposed (refer to Japanese Patent No. 3094403 and JP-A No. 2004-287409).
However, when the particle diameter of a pigment is made minute, the surface area of pigment particles increases, and cohesive force among the pigment particles is strengthened, such that it has been difficult for dispersibility and dispersion stability to be compatible at a high level.
When producing a color filter by using the pigment dispersion composition, a photocurable composition is applied to and dried on a substrate or a substrate with a light blocking layer of a desired pattern previously formed thereon, and thereafter irradiated with radioactive rays (hereinafter referred to as “expose”) through the desired pattern and developed to obtain a pixel in each color. However, in a color filter thus produced, a problem exists in that that residue and scumming easily occur on the substrate at an unexposed portion thereof, or at the light blocking layer, during the developing process, and post-baked pixels after developing are inferior in film coating properties; for example, they are poor in surface smoothness. Moreover, the degree of residue and scumming on the substrate or the light blocking layer and deterioration of surface smoothness tends to become more remarkable as the concentration of the pigment contained in the photocurable composition increases, so that it has been difficult to achieve sufficient color density in a conventional photocurable composition for a color filter.